Semiconductor devices used in radio frequency (RF) power amplifiers are limited by the power dissipation and voltage levels they can handle. RF power amplifiers can subject the transistors used therein to voltages and power levels that could cause failures under overdrive conditions. The transistor terminals that are subject to the most power stress are the output terminals. These are typically the collector in heterojunction bipolar transistor (HBT) processes and the drain in field-effect transistor (FET) processes, in common emitter and common source configurations, respectively. The failure mechanism is dominated by the breakdown of the collector-base junction or the drain-gate junction.
Improving the process to handle a greater breakdown margin is often difficult and may have tradeoffs that may not be desirable. To facilitate improvement of the breakdown issue, the problem may be addressed from a circuit point of view by circuits that detect and protect the main transistor or transistors of the power amplifier under overdrive conditions. In the past, most overdrive protection circuits were built based on the detection of output power or output current level, to control power supplies. This is complicated when implemented on a single chip.
The description in this section is related art, and does not necessarily include information disclosed under 37 C.F.R. 1.97 and 37 C.F.R. 1.98. Unless specifically denoted as prior art, it is not admitted that any description of related art is prior art.